If eligible to use the portal, you will find it in the new portal room.
If you are looking in SW, it is inside the Mage Tower.
If you are looking in ORG, it is the door to the left once you enter the front gates (when leaving from Valley of Strength).
SPOTLIGHT ON PORTALS:
https://us.forums.blizzard.com/en/wow/t/spotlight-on-portals/118521/3